If you check your probes spec sheet, you'll find out how much of a
load it was presenting to the circuit.

When you do a proper oscillator design, you check oscillation drive
level and margin, as well as the load capacitance.  This will tell you
how much additional load the circuit could support.  Most of the
crystal makers have good tech notes on how to do this.

It seems that most hobbyists and an alarming (IMHO) number of
commercial designs do not do a proper oscillator design.

If you want to check for oscillation, a shortwave receiver tuned to
the proper frequency is a big help.  You can probe the VCC line of the
chip and pick up the signal.

Probing the crystals metal can will work if the can was left
ungrounded. That's not a good idea either, but many systems don't
ground them.
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